The artisans in the coatings art have sought, throughout the history, to produce coating compositions, which produce coatings that dry or cure quickly upon application, have desired coating properties, such as high degree of adherence to a wide variety of underlying substrates, increased water and solvent resistance, high degree of durability and gloss. Simultaneously such compositions are also expected to permit the user to efficiently apply such coatings with conventional application means, such as spray guns, paint brushes or paint rollers preferably under ambient conditions. In addition to the foregoing desired coating composition characteristics, there is an increasing expectation and in most countries legally mandated requirement, that such coating compositions do not adversely affect the air quality by releasing excessive amounts of VOCs in the air. As a result, the environmental laws of various countries have reduced, and are expected to reduce even further the amount of VOCs permitted to be released in the air by coating compositions, such as, paints. The low VOC content requirement is of particular importance and relevance for solvent borne coating compositions as compared to waterborne coating compositions. Thus, there exists a need to have low VOC solvent borne coating compositions having most of the foregoing desired coating properties.
Some of the means employed in the past to achieve the foregoing objectives were to reduce the molecular weight of a polymer and to reduce the amount of solvent used during the polymerization of the polymer used in the coating composition. The rationale behind this approach was that by reducing the amount of solvent used during the polymerization, the VOC of the resulting solvent borne coating composition can be reduced. However, there are practical limits to reducing the amount of solvent used during the polymerization of a conventional polymer, typically to no less than 20 weight percent based on the total weight of the coating composition. If attempted, the resulting coating compositions become too viscous and therefore become too difficult to apply over surfaces.
Chang et al. in U.S. Pat. No. 4,652,605 (hereafter the '605 patent) attempted to solve this problem by utilizing a low molecular weight polymeric reaction product resulting from vinyl addition polymerization of a vinyl monomer component of which at least 50 percent by weight is an active hydrogen containing monomer. The addition polymerization in the '605 patent is conducted in the presence of a polymeric diluent. Since the composition in the '605 patent utilizes a polymeric product having 50 or more percent by weight of active hydrogen containing monomers, a substantial amount of crosslinking component needs to be mixed with the polymeric reaction product to prepare a pot mix having a workable degree of cure. As a result, such pot mixes have a short pot life. Moreover, the thermosetting compositions containing low molecular weight polymers tend to be soft. The thermosetting composition of the present invention solves this problem by providing for a low VOC thermosetting composition having a low viscosity and extended pot life while still providing desired coating properties.